1. Technical Field
The present invention relates to a method of forming an image and an ink jet recording apparatus.
2. Background Art
An ink jet technique is a printing method with which fine ink droplets are sprayed onto a recording medium such as a paper sheet or a nonporous substrate to create images.
Nonporous substrates, such as polyvinyl chloride films, polyethylene terephthalate (PET) films, acrylic films, polypropylene films, polyimide films, polystyrene films, and other plastic films, tend to repel droplets of water-based inks applied by an ink jet method and it has been difficult to make water-based inks adhere to nonporous substrates. Thus, solvent inks that contain water-insoluble solvents have been typically used.
However, in recent years, there has been an increasing emphasis on environmental pollution regulations and safety of human bodies and thus there are increasing anticipations for water-based inks that can be used on impermeable media.
To address this issue, a recording method with which water-based ink droplets are adhered to a heated nonporous substrate so as to dry the ink droplets in a short time on the nonporous substrate has been employed.
However, an ink that dries fast on a nonporous substrate is likely to cause nozzle clogging as the ink dries inside the ink jet nozzles. Moreover, rapid drying on a nonporous substrate decreases the uniformity of the film, resulting in low gloss. Accordingly, a technique of enhancing the stability by adding a water-soluble solvent is being investigated so that the ink droplets applied on a heated nonporous substrate remain liquid for a very short time.
For example, JP-4520871-B1 (JP-2005-220352-A) discloses an image printing system in which an ink jet water-based ink containing, at least one volatile cosolvent having a boiling point of 285° C. or lower in a total amount of 5% to 50% by weight is used to print an image on a nonporous substrate and then the printed image is heated. According to this proposal, printing can be conducted on a nonporous substrate because the water-based ink shows an acceptable level of adhesion to the nonporous substrate.
However, according to this proposal, ink droplets come to spread on the nonporous substrate during the period from immediately after application of the ink droplets to the nonporous substrate to the time the ink is heated. This results in ink bleeding at color border portions where different colors lie adjacent to each other and it has been difficult to obtain high-quality images.
In sum, there has been neither an ink jet water-based ink set that can satisfactorily form high-gloss, high-resolution images free of bleeding on a nonporous substrate nor a satisfactory ink jet image forming technique with which an ink can be strongly fixed to a nonporous substrate and nozzle clogging is avoided even when the device is left unused for a long time.